M. Heydari-Malayeri - Paris Observatory

The complex notation for the → Fourier series of a function
f(x). Using → Euler's formulae, the function can be
written in cimplex form as
f(x) = Σ cn einx (summed from -∞ to ∞),
where the → Fourier coefficients are
cn = (1/2π)∫ f(x) e-inx dx (integral from -π to
+π).